1. Field of the Invention
The present invention relates to a pig casting machine comprising an endless conveyor belt, on which pig casting molds are fastened, for transporting the pig casting molds from a casting station to a pig removal station and vice versa, wherein each pig casting mold, with the mold cavity facing upwards, is filled with molten metal as it passes through the casting station, as well as a device for cooling the pig casting molds before, during and/or after casting wherein the pig casting molds are of a thin wall configuration and the rim areas of neighboring pig casting molds overlap.
2. Description of the Related Art
As is known in the art, liquid pig iron is either supplied after tapping in the blast furnace by means of ladles to the steel mill or, if it cannot be processed directly, is cast in the form of ingots, so-called pigs, for storage or for further transport. Pigs of pig iron have different weights depending on the desired application purpose; conventionally, a pig has a weight of 6 kg.
For manufacturing pigs of pig iron, pig casting machines are used. They are conventionally comprised of a casting station, at least one endless conveyor belt as well as a removal station at the first deflection point of the endless belt. Usually, a plurality of thick-walled casting molds are arranged on this endless conveyor belt. The respective casting mold is filled at the casting station with liquid pig iron. The conveying path of the pig casting machine must extend subsequently so far that the liquid iron in the respective pig casting mold is solidified before reaching the first deflection point of the endless conveyor belt and the shrinking enables removal from the casting mold. When passing through the deflection point, the casting molds automatically empty or the pigs are removed by means of a corresponding device from the molds. The pig casting molds or casting molds of known pig casting machines are manufactured of cast iron. In order to accelerate the solidification process of the liquid iron, the casting molds are cooled laterally, and additionally from above, with splashed water.
From German patent document DE 809 948 a pig casting machine for casting light metal and their alloys having correspondingly low melting points is known, wherein the pig casting molds are arranged as an endless belt. It is suggested to form the pig casting molds out of forged metallic material, for example, copper or aluminum or steel, instead of from cast iron. It is described that it is possible in this way to use relatively thin-walled pig casting molds because they can be cooled directly with water before, during, and after casting, for example, by splashing from below.
Based on this prior art, it is an object of the invention to provide a pig casting machine with increased production output, i.e., an increased quantity of cast molten mass per time interval, and at the same time minimal manufacturing costs for the pig casting molds.
This object is solved by at least one endless conveyor belt, on which pig casting molds are fastened, for transport of the pig casting molds from a casting station to a pig removal station and vice versa, wherein each pig casting molds, with the mold cavities facing upwardly, is filled when passing through the casting station with molten metal, as well as a device for cooling the pig casting molds before, during and/or after casting, wherein the pig casting molds have thin walls, characterized in that the pig casting molds are embodied for receiving molten metal having a melting temperature above 1,000xc2x0 C.
The invention is based on the recognition, which has been proven by experiments, that the cooling of the pig casting molds makes it possible, quite in contrast to the decade-old unchanged casting exclusively of light metals with a low melting point, to use for casting heavy metals with melting points above 1,000xc2x0 C. such pig casting molds which are comprised of a heat-resistant material whose melting point is even lower or not significantly higher than the respective melting point of the metal to be cast.
As a result of the minimal wall thickness, the heat conductivity of the pig casting molds is actually no longer of such importance as was the case in the known capacitive cooling. In contrast, the areal cooling across prevents their melting. The molten metal to be cast is, in particular, heavy metal, such as pig iron, which is cast conventionally at temperatures between 1450 and 1520xc2x0 C. The pig casting molds are comprised preferably of copper whose melting point is approximately 1,083xc2x0 C. However, materials with significantly reduced heat conductivity are conceivable, for example, heat-resistant steel, whose melting point, depending on its carbon contents, is within a range of 1,520xc2x0 C.
Accordingly, the criteria for the material of the pig casting mold can be focused on other, essential properties, and, in particular, on the cold or hot forming properties which are decisive for the suitability in a rolling process and a preferred subsequent deep drawing, which allows a cost-efficient manufacture, as well as those mechanical properties at increased temperature which are decisive for the shape stability of the casting mold in use and their insensitivity against cracks. A preferred proposal of the invention suggests thus that the thin-walled precursor material for the pig casting molds is produced by rolling and is subsequently, for example, deep-drawn or die-formed.
According to a first preferred embodiment, it is proposed for achieving an improved cooling situation that carrying baskets on the respective endless conveyor belt are fastened for receiving the individual pig casting molds, wherein the carrying baskets are designed such that they are only partially in supporting contact with the pig casting molds. For this purpose, on the one hand, the inner contour of the carrying baskets is matched approximately to the outer contour of the pig casting molds and, moreover, the inner surface of the carrying baskets is provided with support pins for a point support of the thin-walled pig casting molds, wherein the diameter of the support pins on the carrying basket is not greater than the wall thickness of the pig casting mold. Accordingly, this fulfills the requirements in regard to ensuring a sufficient shape stability of the thin-walled pig casting mold as well as an unimpaired cooling as a result of the point support action.
The carrying basket can also be embodied as a grate basket which supports the respective pig casting mold like a net. In this connection, the configuration and the material for the support medium are to be selected such that they will not counteract a minimal elastic deformation of the pig casting mold as a result of the own weight of the pig. With this elastic deformation and thus minimal widening of the mold, loosening of the pig at the removal station is assisted.
The carrying basket itself can have rolls which run along guide rails. According to another embodiment, the basket is suspended by corresponding securing means in two parallel extending chains.
By means of the carrying basket it is possible to form the walls of the respective pig casting mold so as to be very thin. Casting molds with thin wall thicknesses have the advantage that the risk of fracture formation as a result of thermal stresses is minimized. With reduced wall thickness, however, the shape stability decreases, wherein this disadvantage is compensated by the support action of the carrying basket. As a result of only partial support by means of the support pins or the grate, cooling of the pig casting molds and thus of the cast body by splashing or immersion in a bath is not significantly impaired. In the embodiment of the carrying basket with support pins the diameter of the support pins on the carrying basket should correspond at most to the wall thickness of the pig casting mold so that the cooling at the points of attack of the support pins is not impaired. As a whole, a shape-stable pig casting mold with beneficial cooling properties is provided. The molten mass solidifies quicker, the circulating speed of the endless belt can be increased, and the quantity of molten mass cast per time interval is thus increased.
As an alternative, when the circulating speed remains unchanged, the belt can be configured to be shorter and thus to be less expensive.
As a second embodiment it is proposed to provide the overlap area of the rims of neighboring pig casting molds with a refractory material, wherein preferably the casting mold rim area at the hot side is formed in the overlap area such that a depression for receiving a refractory material results. Starting in this depression, anchoring means for the refractory material are provided.
Because there is no sufficient heat removal possible for the upper one in the area of overlap of two neighboring pig casting molds by splashing with water from below, in this way heat protection of the rim. surface facing the hot side is provided. This solution has the advantage that as a result of the refractory material the use of a cooling water spray in the overlapping area can be reduced and the splash danger as a result of water entering the interior of the pig casting molds can be reduced.
In a preferred embodiment, the pig casting molds are made of laminated material wherein for the layer facing the hot side a material is selected whose melting point is higher than that of copper, in particular, a heat-resistant steel, and for the layer at the cooling side the highly conductive and fracture-resistant copper is selected. The laminated material is preferably manufactured by rolling or explosive cladding with subsequent deformation, for example, by deep drawing, die-forming or the like.
As a whole, the wall thicknesses of the pig casting molds should be in the range between 3 to 20 mm and the ratio of the weight of the pig casting molds to the weight of the pig should be in the range of 0.5 to 2. Conventional pigs of pig iron, in which only the heat dissipation through the metal wall (so-called capacitive cooling) is used, have in contrast to this a weight ratio pig casting mold/pig of much greater than 1, typically of 6.
As a further preferred embodiment it is proposed that a pig casting mold has a plurality of individual casting pans or mold cavities. The pig casting mold can also have a parallelepipedal bottom surface or parallelepipedal casting pans which provides a great advantage in regard to the manufacture of the casting molds.
According to a preferred embodiment, the pig casting molds are cooled from below before, during and after the casting process up to the point of removal of the solidified pig, preferably by areal splashing of cooling water or a water/air mixture. The jet nozzles, depending on the locally required cooling efficiency, can be arranged closely or less closely to one another. When spray cooling, the greater part of the sprayed water evaporates at the underside of the pig casting molds. Drops of water that is not evaporated is collected in a collecting trough and is reused. The collecting trough forms at the same time a housing for removal by vacuum and optionally condensation of the resulting water vapor. An auxiliary cooling device between the removal station and the casting station is possible, but not necessarily required because of the reduced stored heat of the thin-walled casting molds. Moreover, cleaning devices and/or devices for the application of mold coating for the empty pig casting molds can be provided.
According to the invention, the endless belt, in contrast to conventional configurations, is not to be provided with an upper and a lower run but is to be configured horizontally in the way of a carousel. The casting molds are moved in this connection along the carousel arrangement about a circular path of less than 360xc2x0 by filling them at the casting station with molten mass, transporting them on the circular path, and removing them at the removal station, which is arranged shortly before the casting station. For this purpose, the casting molds are rotated or tilted by 180xc2x0. A cooling device in the form of jet nozzles and/or a cooling water collecting trough is arranged such that it begins shortly before the casting station and extends up to the removal station. It is possible, if needed, to use the water collecting trough for the water drops or the condensed water as an immersion tub. As a whole, when employing this configuration, the number of employed pig casting molds is reduced and the use of time is optimized.
As a preferred embodiment it is proposed to design the pig casting molds of a double-wall configuration and to cool them by means of flow-through water cooling. In this connection, in the carousel arrangement a ring distribution line is provided which rotates correspondingly together with the pig casting molds in the horizontal carousel arrangement and is supplied by a rotating line in the center of the carousel, wherein the ring distribution line has hoses which, in turn, supply cooling cross-sections which are positioned in intermediate spaces of the double-wall pig casting molds.